Aidan,
it seems that you're one of those who are more concerned about having to forfeit a couple of Dollars towards such a project than the benefits for the following generation.

individual,
>it seems that you're one of those who are more concerned about having to forfeit a
>couple of Dollars towards such a project than the benefits for the following generation.
Your perception is incorrect. You need to get rid of it now, because it's preventing you from thinking objectively about what I'm saying.

I am not dismissing anything on cost alone. But nor do I think it should be disregarded. My concerns, in order of priority are:

EFFECTIVENESS: You should learn about the conditions that cause rain, because they're not what you assume them to be. And there's no point spending gigabucks on a scheme that won't work.

ENVIRONMENT: So much of our natural environment's gone that we shouldn't have the luxury of disregarding it any more. We need to consider the environmental impacts of everything we do, and switch to an alternative course of action (or at least offset the damage) if it threatens a species or ecosystem.

DEMAND: You may not like to hear this, but the limiting factor of how much is grown isn't what's technically possible, but what's cost effective - and that depends as much on demand as it does on supply. Unless and until there is an increase in demand, it's a zero sum game. Devoting massive government resources to expanding farming in one area is very unfair if it's at the expense of farmers in another area. Maybe after populations grow, diverting rivers will be a viable option that could benefit us all. But at the moment it's clearly not.

EFFICIENCY: Schemes need to compared to other options. For instance, more farming around the Gulf of Carpentaria (making use of Artesian water) could be a much more cost effective way of expanding agriculture than diverting rivers would. Similarly, more use of greenhouses (consuming very little because most of their water's reused) can be a much more cost effective way of coping with water shortages.

Has any one considered how the city of Kalgoorlie gets its water
It should prove it can be done
Why are we thinking in terms of only massive water transfer
In fact many different transfer methods can be used and the massive ones the country needs will follow, in time
Harvesting storm water before it enters the sea is just one way we can move water

Aha, Aidan,

Neo liberalism is alive, as per the article on OLO by Rob Stewart - 20/12/2018. That's one tough read, and the message is disturbing.
So, Aidan, you're right of course, economics, economics, you can't survive without it, and you can't control the beast - all you can do is try to make the best of it, and hopefully hope, in huge letters, that one day (and I most certainly hope soon) a greater sanity will, as it duly must, prevail, and the children of the world may at last awaken to a new dawn, a new and embracing euphoria filled with hope and promise of no bombs, no scary cultural and social protocols designed to inhibit, to quell, to crush the masses into a submission alien to all species except Man, to accept the Order of Those who have the inalienable right to talk to God and to hurtle that crushing and demoralizing message down on the heads of the sheeple.

Sometimes, Aidan, one must do what is right, for the future, irrespective of the vested interests of those who want to control everything - everything you see, read, are told, and yea, what indeed you are allowed to believe.

The outlined project is one for the future, for hope, for freedom, for an ultimate good - for people.

Look at the world and think - is this how it must be? Must Man destroy everything in pursuit of the mighty dollar, or can we rise above and beyond and strive with every cell of our being to leave a world that future generations can enjoy fully, and can share fully with all the myriad of life we are so very blessed to be able to enjoy, even from a great distance - in the certain comfort that they are there, they were saved the fate of the Dodo, the Tassie Tiger, and so very many, many more. Our watch, 20th and 21st Century watch, has thus-far been such an indictment on human folly. We can and must do better.

Aus is getting a Space Agency, Branson is offering zips into near space, and NASA and the Ruskie's are heading for colonies on Mars.
Exodus the fallen garden.
How terribly smart we are - not content with what's in our laps, smashing it, like so many spoiled and conceited undisciplined children, moving on, pushing aside. Me, me!
Hell is already here.

more farming around the Gulf of Carpentaria
Aidan,
Cyclonic weather wipes out any produce. The most useful thing to do in the Gulf country would be to build dams to divert water inland. Aqua culture would probably be a winner there instead of the overfishing on the GBR.
We must have large amounts of fresh water run into the sea because that's how Nature works but nowadays we have too much run-off because urban infrastructure prevents soakage so, this excess can go inland.